Storage capacity for phosphorus during growth and maturation in a brown alga Sargassum macrocarpum

Improved coastal management has decreased anthropogenic nutrient input over the past few decades, leading to phosphorus depletion. It has been hypothesized that phosphorus depletion in coastal environments leads to declines in macroalgae abundance. Perennial canopy-forming temperate macroalgae can experience the effects of limited phosphorus availability during seasonal phosphorus depletion periods. When nutrients are sufficient, they are stored in algal tissues after luxury uptake and are available to support growth during phosphorus depleted conditions. Cultivation of mature and actively growing juvenile brown alga (Sargassum macrocarpum) under different nutrient conditions provided individuals with different tissue nutrient concentrations. The maximum photosynthetic rates of these individuals were examined under nutrient-depleted conditions to evaluate storage capacity, which we defined as the amount of stored phosphorus that can support maximum growth. Maximum photosynthetic rate was used as a proxy for maximum growth rates. The experiments revealed that growth rates of juveniles increased when stored phosphorus content was high. In contrast, the maximum growth rates tended not to increase with an increase in stored phosphorus content in mature individuals. The phosphorus storage capacities for juvenile and mature in dividuals were approximately 19 and more than 16 weeks, respectively, suggesting that individual alga can endure several months of phosphorus depletion. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

Improved coastal management has led to phosphorus depletion in coastal environments, potentially impacting the abundance of macroalgae. Juveniles and mature individuals of the brown alga species Sargassum macrocarpum have different phosphorus storage capacities, with higher stored phosphorus content benefiting the growth rates of juveniles. The experiments suggest that individual alga can endure several months of phosphorus depletion due to their phosphorus storage capacity.